Cable tray bonding???

[danielc4514]

Hi all, been a while since been on here.
i have just completed all my 2365 level 2 exams and am completing my practical tomorow..... I have cable tray supporting an swa cable and obviously the tray needs bonding..... I was told by one electrician that this can be in 2.5mm however i have always been told it is a minimum of 4mm when bonding?? What is the correct answer here?? Does there need to be a bonding tag on this?? I also have trunking would this require the same?
Also in my practical exam i have a ring final, radial and a lighting circuit.... There is a 6,16,20 and 32 amp breaker in the consumer unit.... I will be using the 6,16 and 32... I believe they have put the extra breaker in as the radial could go on either depending on how its run.... Can i leave the 20 amp in unconnected? And would i put spare, unused or something else for that slot on my test certificate??

Thanks all

 

[danielc4514]

The radial is swa clipped to the tray... Am i correct in saying this will be on the 16amp as the tutor yesterday told us this was the case?

 

[derek]

Cable tray only needs bonding if it is an extraneous conductive part. Trunking is normally earthed as it often has single conductors with insulation but no additional sheathing. Cable tray is not an exposed conductive part if it has class two cables on it so doesn't always require earthing, but I could be wrong as I always follow the design I am given on site and don't get overly involved in the design aspect

 

[Richard Burns]

I do not know the specifics of the exam but in general tray, that is not connected to earth potential by nature of its construction, is neither an extraneous-conductive-part nor an exposed-conductive-part.
Therefore it would not need any connection to earth.
Having said that the general approach that appears to be employed is to assume that if a cable were damaged so it made the tray live this would be dangerous and so the tray should be earthed as an exposed-conductive-part.
Trunking is an exposed-conductive-part and should be earthed.

The minimum size for a protective conductor that is not mechanically protected and is a single unenclosed cable is 4mm².

If your tutor has said that the SWA radial on tray willbe using the 16A breaker then presumably that is the case, is there any reason why you doubt him?
If you consider the load the circuit may be intended to carry and the current carrying capacity of the cable used you should be able to determine if the 20A breaker would be suitable. Ib<In<Iz.

 

[danielc4514]

I do not know the specifics of the exam but in general tray, that is not connected to earth potential by nature of its construction, is neither an extraneous-conductive-part nor an exposed-conductive-part.
Therefore it would not need any connection to earth.
Having said that the general approach that appears to be employed is to assume that if a cable were damaged so it made the tray live this would be dangerous and so the tray should be earthed as an exposed-conductive-part.
Trunking is an exposed-conductive-part and should be earthed.

The minimum size for a protective conductor that is not mechanically protected and is a single unenclosed cable is 4mm².

If your tutor has said that the SWA radial on tray willbe using the 16A breaker then presumably that is the case, is there any reason why you doubt him?
If you consider the load the circuit may be intended to carry and the current carrying capacity of the cable used you should be able to determine if the 20A breaker would be suitable. Ib<In<Iz.

the reason for bonding it is as you said, if there was a fault and for some reason it did become live there wouldnt be any protection.
I only second guess him as i have had 4 tutors now and they all contradict each other and makes it very difficult for me as a student to know what is the correct procedure. I was told by the last tutor that 2.5mm earthing will be fine, the tutor i have now is very hard work and will not tell us anything. We asked him before the exam about a bonding tag being needed and he refused to answer it and said i must look in the book during the practical exam.

maybe ill change the bonding to 4mm tomorow.

thanks for your replies lads

 

[shanky887614]

Hi all, been a while since been on here.
i have just completed all my 2365 level 2 exams and am completing my practical tomorow..... I have cable tray supporting an swa cable and obviously the tray needs bonding..... I was told by one electrician that this can be in 2.5mm however i have always been told it is a minimum of 4mm when bonding?? What is the correct answer here?? Does there need to be a bonding tag on this?? I also have trunking would this require the same?
Also in my practical exam i have a ring final, radial and a lighting circuit.... There is a 6,16,20 and 32 amp breaker in the consumer unit.... I will be using the 6,16 and 32... I believe they have put the extra breaker in as the radial could go on either depending on how its run.... Can i leave the 20 amp in unconnected? And would i put spare, unused or something else for that slot on my test certificate??

Thanks all

it depends though on the scenario, does it go outside? if so it might need to be a lot bigger

 

[Simonslimline]

the reason for bonding it is as you said, if there was a fault and for some reason it did become live there wouldnt be any protection.
I only second guess him as i have had 4 tutors now and they all contradict each other and makes it very difficult for me as a student to know what is the correct procedure. I was told by the last tutor that 2.5mm earthing will be fine, the tutor i have now is very hard work and will not tell us anything. We asked him before the exam about a bonding tag being needed and he refused to answer it and said i must look in the book during the practical exam.

maybe ill change the bonding to 4mm tomorow.

thanks for your replies lads

Don't get Earthing & bonding mixed up mate.

They are two completely separate things.

 

[Richard Burns]

Safety electrical connection: do not remove labels are only required where you are connecting main bonding to an extraneous-conductive-part.
Unless you are running a 10mm² cable back to the MET then the label is not needed.

 

[shanky887614]

the reason for bonding it is as you said, if there was a fault and for some reason it did become live there wouldnt be any protection.
I only second guess him as i have had 4 tutors now and they all contradict each other and makes it very difficult for me as a student to know what is the correct procedure. I was told by the last tutor that 2.5mm earthing will be fine, the tutor i have now is very hard work and will not tell us anything. We asked him before the exam about a bonding tag being needed and he refused to answer it and said i must look in the book during the practical exam.

maybe ill change the bonding to 4mm tomorow.

thanks for your replies lads

i can't recommend this highly enough, it really helped me prep for my am2

i think there will be a new edition now, i like it better than the onsite guide and its more useful as it covers pfc etc that the onsite doesnt and it goes into more detail

it is very useful in testing for example it explains best practises in finding things like bridged rings etc

 

[Knobhead]

I don’t know what the thoughts of others are. To me and this is what I was taught as an apprentice and I’ve carried it on ever since, the tray should be bonded in the event of a fault. The only exception was if the stand off brackets were welded to the structural steelwork, we still did the bonding out of habit.


To make you chuckle, 16mm² was the minimum bonding conductor allowed under M&Q regs and our company rules. So you’ve just put a couple of 2.5mm² SWA’s on a new galvanized tray. The glands and the tray had to have the 16mm² to them.
It was unsheathed 7/.064 then and was for years after metrification, we must have had 2000 yards of it in stores.
I once got two drums mixed up, ever tried crimping hard drawn copper?